Process for preventing polymerization of vinyl compound

ABSTRACT

There is disclosed a process for preventing the polymerization of a vinyl compound which comprises allowing water in an amount of 0.05 to 5% by weight based on the vinyl compound or a corrosion inhibitive substance selected from an alcohol, an inorganic acid or its salt, an aromatic carboxylic acid or its salt and a zinc-containing salt in an amount of preferably 0.01 to 5% by weight based on the same, to coexist with a metallic salt of dithiocarbamic acid, in preventing the polymerization of the vinyl compound with the metallic salt of dithiocarbamic acid. The above process makes it possible to effectively inhibit the polymerization of acrylic acid, methacrylic acid, etc. in the distillation system, etc. of the production process for the above acids as well as the corrosion of the equipment and machinery to be used therein and also to assure long-term stable continuous operation of the equipment and machinery.

TECHNICAL FIELD

The present invention relates to a process for preventing thepolymerization of a vinyl compound. More particularly, it pertains to aprocess for preventing the polymerization of a vinyl compound whichprocess is capable of effectively inhibiting the polymerization ofacrylic acid, methacrylic acid or the like in the distillation system,etc. of the production process for the above-mentioned acid, etc. aswell as the corrosion of the equipment and machinery to be used thereinand at the same time, enables long-term stable continuous operation ofthe equipment and machinery.

BACKGROUND ART

It has heretofore been known that a vinyl compound such as styrene,acrylic acid, methacrylic acid, an acrylic ester, a methacrylic esterand acrylonitrile has the property of liability to polymerization bylight, heat or the like. In the production process of theabove-mentioned vinyl compound, various distillation operations are putinto practice for the purpose of separating, recovering, concentratingor purifying the objective vinyl compound. However, the aforesaid vinylcompound is apt to bring about an unfavorable situation such as varioustroubles in the distillation step which finally make it impossible toproceed with a long-term stable continuous operation, since as mentionedabove, the compound is liable to polymerization by light, heat or thelike to form a polymer-like substance.

In order to avoid such a situation, there has heretofore been adopted aprocess in which the distillation operations are put into practice inthe presence of a polymerization inhibitor, which is exemplified byhydroquinone, methoquinone (p-methoxyphenol), p-tert-butyl catechol,tert-butylhydroquinone and phenothiazine. Nevertheless, the actualsituation is that any of the above-mentioned polymerization inhibitorsdoes not necessarily exert sufficient effect on acrylic acid,methacrylic acid and the like because of their extreme liability topolymerization.

Aside from the foregoing, it is known that cupric dibutyldithiocarbamateis a substance which is capable of extremely effectively preventing thepolymerization in liquid phase of acrylic acid, methacrylic acid, etc.,but it has been difficult to employ the substance in an industrialmanufacturing plant because of its fatal disadvantage that it corrodesan equipment made of, for example, SUS 316.

On the other hand, there is proposed a method in which a manganate isemployed as a corrosion inhibitor in combination with a metallic salt ofdithiocarbamic acid. (Refer to Japanese Patent Application Laid-Open No.51403/1993). However, the aforesaid method is not satisfactory becauseof its insufficient corrosion inhibition effect.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide, under suchcircumstances, a process for preventing the polymerization of a vinylcompound which process is capable of efficiently inhibiting thepolymerization of a vinyl compound, especially acrylic acid, methacrylicacid or the like in the distillation system, etc. of the productionprocess for the above-mentioned acid, as well as the corrosion of theequipment and machinery to be used therein, and at the same time,enables long-term stable continuous operation of the equipment andmachinery.

As a result of intensive research and investigation accumulated by thepresent inventors in order to attain the above-mentioned object, it hasbeen found that the object can be attained by paying attention to theexcellent corrosion inhibition effect of a metallic salt ofdithiocarbamic acid typified by cupric dibutyldithiocarbamate and makinguse thereof in combination with a specific corrosion inhibitivesubstance typified by water. The present invention has been accomplishedby the foregoing finding and information.

Specifically, the present invention provides a process for preventingthe polymerization of a vinyl compound which comprises allowing water inan amount of 0.05 to 5% by weight based on the vinyl compound to coexistwith a metallic salt of dithiocarbamic acid, in preventing thepolymerization of the vinyl compound with the metallic salt ofdithiocarbamic acid in the production process of the vinyl compound.

The present invention further provides a process for preventing thepolymerization of a vinyl compound which comprises allowing at least onecorrosion inhibitive substance selected from the group consisting of (a)an alcohol, (b) an inorganic acid or a salt thereof, (c) an aromaticcarboxylic acid or a salt thereof and (d) a zinc-containing salt tocoexist with a metallic salt of dithiocarbamic acid, in preventing thepolymerization of the vinyl compound with the metallic salt ofdithiocarbamic acid in the production process of the vinyl compound.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

As the vinyl compound to which the process of the present invention isapplicable, mention may be made of, for example, styrene, acrylic acid,methacrylic acid, an acrylic ester, a methacrylic ester andacrylonitrile, of which acrylic acid and methacrylic acid areparticularly preferable.

There is used in the process according to the present invention, ametallic salt of dithiocarbamic acid as a polymerization inhibitor forthe above-mentioned vinyl compound. As the metallic salt ofdithiocarbamic acid usable therein, mention may be made of the compoundhaving the structure repersented by the general formula (I) ##STR1##wherein R¹ and R² may be the same as or different from each other andare each a phenyl group or an alkyl group which has 1 to 8 carbon atoms,may be straight-chain or branched and are specifically exemplified bymethyl group, ethyl group, propyl group, butyl group, pentyl group andhexyl group; M stands for a metal such as nickel, zinc, copper, iron anda transition metal (Mn, Co, etc.); and n is the valency of the metal M.

Examples of the metallic salt of dithiocarbamic acid represented by thegeneral formula (I) include cupric dimethyldithiocarbamate, cupricdiethyldithiocarbamate, cupric dipropyldithiocarbamate, cupricdibutyldithiocarbamate, cupric dipentyldithiocarbamate, cupricdihexyldithiocarbamate, cupric diphenyldithiocarbamate, cupricmethylethyldithiocarbamate, cupric methylpropyldithiocarbamate, cupricmethylbutyldithiocarbamate, cupric methylpentyldithiocarbamate, cupricmethylhexyldithiocarbamate, cupric methylphenyldithiocarbamate, cupricethylpropyldithiocarbamate, cupric ethylbutyldithiocarbamate, cupricethylpentyldithiocarbamate, cupric ethylhexyldithiocarbamate, cupricethylphenyldithiocarbamate, cupric propylbutyldithiocarbamate, cupricpropylpentyldithiocarbamate, cupric propylhexyldithiocarbamate, cupricpropylphenyldithiocarbamate, cupric butylpentyldithiocarbamate, cupricbutylhexyldithiocarbamate, cupric butylphenyldithiocarbamate, cupricpentylhexyldithiocarbamate, cupric pentylphenyldithiocarbamate, cuprichexylphenyldithiocarbamate and a nickel salt, a zinc salt, an iron saltan a transition-metal salt (Mn, Co, etc.) each corresponding to thecupric salt exemplified above. Of the above-exemplified metallic saltsof dithiocarbamic acid, cupric dithiocarbamate is preferable and cupricdibutyldithiocarbamate is particularly preferable.

The aforesaid metallic salt of dithiocarbamic acid as a polymerizationinhibitor may be used alone or in combination with at least one othermetallic salt. The amount thereof to be added to the vinyl compound isusually selected in the range of 0.01 to 1, preferable 0.05 to 0.5% byweight based on the vinyl compound. An amount thereof less than 0.01% byweight can not sufficiently exhibit the polymerization inhibitioneffect, whereas that more than 1% by weight can not enhance the effectin proportion to the amount of the inhibitor added, thus causingdisadvantage from the economical point of view.

In order to inhibit the corrosion of the equipment and machinery in theprocess according to the present invention water may be allowed tocoexist with the above-mentioned metallic salt of dithiocarbamic acid.It is necessary in this case to regulate the amount of the coexistingwater to the range of 0.05 to 5% by weight based on the vinyl compound.The amount of water less than 0.05% by weight can not sufficientlyexhibit the corrosion inhibition effect, whereas that more than 5% byweight requires excessively large amount of energy to separate water,thereby causing disadvantage from the economical point of view. Anamount of water preferable from both the viewpoints of corrosioninhibition effect and economical efficiency is in the range of 0.07 to0.5% by weight based on the vinyl compound.

Moreover in order to inhibit the corrosion of the equipment andmachinery in the process according to the present invention, there maybe used a corrosion inhibitive substance comprising at least one memberselected from the group consisting of (a) an alcohol, (b) an inorganicacid or a salt thereof, (c) an aromatic carboxylic acid or a saltthereof and (d) a zinc-containing salt.

As the alcohol to be used as the component (a) in the corrosioninhibitive substance, mention may be made of, for example, a primaryalcohol having 1 to 10 carbon atoms such as methyl alcohol, ethylalcohol, n-propyl alcohol, n-butyl alcohol, isobutyl alcohol, n-octylalcohol and 2-ethylhexyl alcohol, a polyhydric alcohol such as ethyleneglycol; propylene glycol; 1,4-butane diol; and 1,6-hexane diol, and anaromatic alcohol such as phenol, cresol, xylenol, benzyl alcohol andphenethyl alcohol. Of these a polyhydric alcohol is preferable. Examplesof the preferable inorganic acid to be used as the component (b) includean oxoacid, which is specifically exemplified by boric acid, phosphoricacid, nitric acid and sulfuric acid. Of these phosphoric acid isparticularly preferable. Examples of the salt of the inorganic acidinclude a nickel salt, a zinc salt, a copper salt, an iron salt and asalt of any of various transition metals (Mn, Co, etc.)

Examples of the aromatic carboxylic acid to be used as the component (c)and a salt thereof include benzoic acid, naphthalenecarboxylic acid,salicylic acid, p-hydroxybenzoic acid, oxynaphthoic acid, and a nickelsalt, a zinc salt, a copper salt, an iron salt and any of varioustransition metals (Mn, Co, etc.) each of the aforesaid aromaticcarboxylic acid. Examples of the zinc-containing salt to be used as thecomponent (d) include zinc formate, zinc acetate and zincdithiocarbamate.

The above-exemplified corrosion inhibitive substances may be use aloneor in combination. The amount thereof to be used is preferably in therange of 0.001 to 5% by weight based on the vinyl compound. An amountthereof less than 0.001% by weight can not sufficiently exhibit thecorrosion inhibition effect, whereas that more than 5% by weight can notenhance the effect in proportion to the amount of the inhibitor added,causing a fear of other disadvantage. In order to effectively carry outcorrosion inhibition without causing any other disadvantage, the amountof the corrosion inhibitive substance to be used is preferably in therange of 0.01 to 3% by weight, particularly preferably 0.1 to 1% byweight based on the vinyl compound.

In the case where an oxoacid, especially phosphoric acid among theinorganic acid is used as a corrosion inhibitive substance, the amountof phosphoric acid is preferably at least 0.1 (weight ratio) based onthe aforesaid metallic salt of dithiocarbamic acid, especially cupricdithiocarbamate.

In the process according to the present invention, the aforesaidpolymerization inhibitor may be incorporated, as desired, with an otherknown polymerization inhibitor such as hydroquinone, methoquinone,p-tert-butyl catechol, tert-butylhydroquinone and phenothiazine to theextent that the object of the present invention is not impaired thereby.

In the process according to the present invention, the treatmenttemperature of the vinyl compound containing the above-mentionedmetallic salt of dithiocarbamic acid and water, or the metallic salt ofdithiocarbamic acid and the corrosion inhibitive substance variesdepending upon the type of the vinyl compound, but in the case ofacrylic acid or methacrylic acid, it is usually in the range of 50° to130° C. The polymerization inhibition effect and corrosion inhibitioneffect are sufficiently exhibited when the treatment temperature iswithin the aforesaid range.

In the following, the present invention will be described in more detailwith reference to the working examples, which however shall not beconstrued to limit the invention thereto.

COMPARATIVE EXAMPLE 1

A 500 mL (milliliter) separable flask equipped with a reflux tube wascharged with a SUS 316-made test piece (40×15×3 mm) which had beensubjected to oxidation film treatment and 200 mL of acrylic acid, andthe content in the flask was brought into a reflux state, while theflask inside temperature was kept at 110° C. under reduced pressure.Into the flask was continuously fed a solution of cupricdibutylthiocarbamate as polymerization inhibitor in acrylic acid havinga water content of 210 ppm by weight, said solution having aconcentration of 3500 ppm by weight based on the acrylic acid at a rateof 40 mL/hour, while the solution in the flask was continuouslywithdrawn at the same rate. As a result, the weight loss of the testpiece due to corrosion during a period of 10 days was 0.334 g.

COMPARATIVE EXAMPLE 2

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that phenothiazine wasused as a polymerization inhibitor in place of cupricdibutyldithiocarbamate. As a result, any weight loss of a test piece dueto corrosion during a period of 10 days was not recognized. It isunderstood by the comparison between Comparative Examples 1 and 2 thatcupric dibutyldithiocarbamate is corrosive.

COMPARATIVE EXAMPLE 3

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of manganese acetate at a concentration of 3,630 ppmby weight based on acrylic acid along with the cupricdibutyldithiocarbamate at a concentration same as in Comparative Example1 in acrylic acid having a water content of 240 ppm by weight. As aresult, the weight loss of the test piece due to corrosion during aperiod of 10 days was 0.080 g.

Examples 1 and 2

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that the water contentin the acrylic acid was set at 910 ppm by weight (Example 1) and 1,740ppm by weight (Example 2) each based on acrylic acid. As a result, theweight loss of the test piece due to corrosion during a period of 10days was 0.005 g and at most 0.001 g, respectively.

Example 3

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of zinc dibutyldithiocarbamate at a concentration of3,500 ppm by weight based on acrylic acid along with the cupricdibutyldithiocarbamate at a concentration same as in Comparative Example1 in acrylic acid having a water content of 970 ppm by weight. As aresult, the weight loss of the test piece due to corrosion during aperiod of 10 days was 0.001 g.

Example 4

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of ethylene glycol at a concentration of 10,000 ppmby weight based on acrylic acid along with the cupricdibutyldithiocarbamate at a concentration same as in Comparative Example1 in acrylic acid having a water content of 120 ppm by weight. As aresult, the weight loss of the test piece due to corrosion during aperiod of 10 days was 0.003 g.

Example 5

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of zinc phosphate at a concentration of 1,700 ppm byweight based on acrylic acid along with the cupricdibutyldithiocarbamate at a concentration same as in Comparative Example1 in acrylic acid having a water content of 140 ppm by weight. As aresult, the weight loss of the test piece due to corrositon during aperiod of 10 days was 0.009 g.

Example 6

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of phosphoric acid at a concentration of 8,500 ppm byweight based on acrylic acid along with the cupricdibutyldithiocarbamate at a concentration same as in Comparative Example1 in acrylic acid having a water content of 322 ppm by weight. As aresult, the weight loss of the test piece due to corrosion during aperiod of 10 days was 0.001 g.

Example 7

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of boric acid at a concentration of 3,300 ppm byweight based on acrylic acid along with the cupricdibutyldithiocarbamate at a concentration same as in Comparative Example1 in acrylic acid having a water content of 200 ppm by weight. As aresult, the weight loss of the test piece due to corrosion during aperiod of 10 days was 0.001 g.

Example 8

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of benzoic acid at a concentration of 10,000 ppm byweight based on acrylic acid along with the cupricdibutyldithiocarbamate at a concentration same as in Comparative Example1 in acrylic acid having a water content of 135 ppm by weight. As aresult, the weight loss of the test piece due to corrosion during aperiod of 10 days was 0.002 g.

The results of the above-mentioned comparative examples and examples arecollectively given in Table 1.

No polymerirzation of acrylic acid was recognized in any of the Examples1 to 8 and Comparative Example 1 and 3. However, a sign ofpolymerization of acrylic acid was recognized in Comparative Example 2.

                  TABLE 1-1    ______________________________________    Content, ppm by weight    based on acrylic acid                   Comparative                             Comparative                                       Comparative                   Example 1 Example 2 Example 3    ______________________________________    Cupric dibutyl-                   3,500     --        3,500    dithiocarbamate    Phenothiazine  --        3,500     --    Corrosion    inhibitor    (ppm)    Water          210       90        240    Zinc dibutyldithiocarbamate                   --        --        --    Ethylene glycol                   --        --        --    Zinc phosphate --        --        --    Phosphoric acid                   --        --        --    Boric acid     --        --        --    Benzoic acid   --        --        --    Manganese acetate                   --        --        3,630    Weight loss of SUS 316-test                   0.334     <0.001    0.080    piece for 10 days (g)    ______________________________________

                  TABLE 1-2    ______________________________________    Content, ppm by weight    based on acrylic acid                 Example 1                          Example 2                                   Example 3                                          Example 4    ______________________________________    Cupric dibutyl-                 3,500    3,500    3,500  3,500    dithiocarbamate    Phenothiazine                 --       --       --     --    Corrosion    inhibitor    (ppm)    Water        910      1,740    970    120    Zinc         --       --       3,500  --    dibutyldithiocarbamate    Ethylene glycol                 --       --       --     10,000    Zinc phosphate                 --       --       --     --    Phosphoric acid                 --       --       --     --    Boric acid   --       --       --     --    Benzoic acid --       --       --     --    Manganese acetate                 --       --       --    Weight loss of                 0.005    <0.001   0.001  0.003    SUS 316-test    piece for 10 days (g)    ______________________________________

                  TABLE 1-3    ______________________________________    Content, ppm by weight    based on acrylic acid                 Example 5                          Example 6                                   Example 7                                          Example 8    ______________________________________    Cupric dibutyl-                 3,500    3,500    3,500  3,500    dithiocarbamate    Phenothiazine                 --       --       --     --    Corrosion    inhibitor    (ppm)    Water        140      322      200    135    Zinc         --       --       --     --    dibutyldithiocarbamate    Ethylene glycol                 --       --       --     --    Zinc phosphate                 1,700    --       --     --    Phosphoric acid                 --       8,500    --     --    Boric acid   --       --       3,300  --    Benzoic acid --       --       --     10,000    Manganese acetate                 --       --       --     --    Weight loss of                 0.009    0.001    0.001  0.002    SUS 316-test    piece for 10 days (g)    ______________________________________

Example 9

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of phosphoric acid at a concentration of 50 ppm byweight based on acrylic acid along with the cupricdibutyldithiocarbamate at a concentration of 500 ppm by weight based onthe same in acrylic acid and that the flask inside temperature was keptat 130° C. instead of 110° C. As a result, the weight loss of the testpiece due to corrosion during a period of 10 days was 0.001 g.

Example 10

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of phosphoric acid at a concentration of 4,000 ppm byweight based on acrylic acid along with the cupricdibutyldithiocarbamate at a concentration of 15,000 ppm by weight basedon the same in acrylic acid and that the flask inside temperature waskept at 130° C. instead of 110° C. As a result, the weight loss of thetest piece due to corrosion during a period of 10 days was 0.022 g.

Examples 11 to 21

The procedure in Comparative Example 1 was repeated to carry out theexperiment on polymerization and corrosion except that into the flaskwas fed a solution of phosphoric acid at a concentration shown in Table2 along with the cupric dibutyldithiocarbamate at a concentration alsoshown in Table 2 in acrylic acid. As a result, the weight loss of thetest piece due to corrosion during a period of 10 days was 0.001 g foreach of the examples.

                  TABLE 2    ______________________________________               Content of cupric                             Content of phosphoric               dibutyldithiocarbamate                             acid               (ppm by weight) based                             (ppm by weight) based               on acrylic acid                             on acrylic acid    ______________________________________    Example 11 300           100    Example 12 300           400    Example 13 500           600    Example 14 3500          100    Example 15 3500          400    Example 16 3500          900    Example 17 3500          4000    Example 18 3500          8500    Example 19 7000          8500    Example 20 10000         1300    Example 21 15000         20000    ______________________________________

INDUSTRIAL APPLICABILITY

As described hereinbefore, according to the present invention, it ismade possible to effectively inhibit the polymerization of acrylic acid,methacrylic acid or the like in the distillation system, etc. of theproduction process for the above-mentioned acid, etc. as well as thecorrosion of the equipment and machinery to be used therein and at thesame time, to assure long-term stable continuous operation of theequipment and machinery.

We claim:
 1. A process for preventing the polymerization of a vinylcompound which comprises allowing water in an amount of 0.05 to 5% byweight based on the vinyl compound to coexist with a metallic salt ofdithiocarbamic acid, in preventing the polymerization of the vinylcompound with the metallic salt of dithiocarbamic acid in the productionprocess of the vinyl compound.
 2. The process according to claim 1wherein the vinyl compound is acrylic acid or methacrylic acid.
 3. Theprocess according to claim 1 wherein the metallic salt of dithiocarbamicacid is cupric dibutyldithiocarbamate.